Deep well treatment



Patented Mar. 25, 1952 DEEP WELL TREATMENT Paul H. Cardwell, Albert W.Coulter, Jr., and Harry H. Jones, Tulsa, Okla., assignors to The DowChemical Company, Midland, Mich., a corporation of Delaware ApplicationApril 21, 1949, Serial No. 88,802

2 Claims. (Cl. 166-21) The invention relates to Vmethods of treatingdeep wells, such as those drilled into the earth for oil or other fluid.It more particularly concerns an improved method of preventing theintermixing of a liquid agent which is heavier than, and immiscible withanother liquid on which it is superimposed on being introduced into awell through the usual tubing string.

In the construction and maintenance of a deep well, particularly onedrilled for oil, it is sometimes desirable or necessary to deliver acharge of a liquid agent of one kind or another into the well throughthe usual tubing string without mixing the liquid agent with anotherliquid already in the tubing string or introduced thereinto ahead of theliquid agent.

Liquid agents that are lighter than those on which they are superimposedin a well tubing string generally remain in their same relativepositions While standing in or traversing the bore of the tubing stringwithout special precautions being taken to prevent intermixing. On theother hand, liquid agents that are heavier than and immiscible withthose on which they are superimposed in a well tubing string becomeintermixed on standing in or traversing the bore of the tubing stringunless special precautions are taken to prevent it.

Heretofore, in attempting to keep two superimposed liquids separatedfrom ea-ch other in the tubing string in a well, when the upper liquidis heavier than and immiscible with the lower one, a more or lessresilient cylindrical plug, usually of rubber, that makes a slidingsealing t in the tubing bore, has been used. In use, the plug isinserted in the tubing string ahead of the heavier liquid to be keptseparated from the lighter one below it. However, this method ofseparating the heavier liquid from the lighter one has certaindisadvantages which limit its usefulness. One of the disadvantages isthat the plugs available do not always conform to all the irregularitiesencountered on traversing the bore of a tubing string. As a resultby-passing of liquid occurs around the plug, thus allowing the one liquid to mix with the other. In some instances, the plugs become damagedin traversing the bore of the tubing string, as when passing from onetubing length to another across the collars connecting each length oftubing in the string. After being damaged, the plugs usually do notprevent the one liquid from being intermixed with the other. In additionto the foregoing disadvantages, the conventional tubing plug has thedisadvantage often-times of being in the way after having served itspurpose and a removal operation is thereby necessitated as by drilling.

In so far as we are aware, there is no satisfactory commerciallyavailable method of preventing the intermixing of a liquid which isheavier than an" immiscible with another on which it is superimposed onbeing introduced into a well through the usual tubing string.Accordingly, it is the principal object of the invention to provide amethod fullling this need.

We have discovered that by introducing into the tubing string, ahead 'ofthe liquid agent to be supported on a column of a lighter liquid thereinwith which the liquid agent is immiscible, another liquid that isheavier than and immiscible with the liquid agent and miscible with theliquid of the liquid column intermixing of the liquid` agent with theliquid of the liquid column is prevented.

For example, in an oil well provided with the usual tubing stringcontaining a column of oil, a quantity of a relatively heavyoil-miscible liquid is introduced into the tubing string onto the oilcolumn therein ahead of the liquid agent which is to be kept separatedfrom the oil column. The oil-miscible liquid thus introduced, descendsinto the oil forming a solution therewith, the speciiic gravity of whichis thereby raised to a value exceeding that of the liquid agent to bekept separated from the oil column. The liquid agent is subsequentlyintroduced, and, being lighter than the solution on the oil column,iloats thereon as long as the speciiic gravity of the solution remain-sabove that of the liquid agent. Although vthe specific gravity of thesolution declines in time as the relatively heavy liquid diffuses intoand is diluted by the lighter liquid, nevertheless, suicient time is hadto permit the relatively heavy liquid agent to be lowered through atubing string behind a lighter liquid column therein without intermixingof the two liquids.

The following examples are illustrative of th application of theprinciple of the invention in preventing the intermixing of a relativelyheavy liquid agent supported in a tube as a liquid column on a column ofa lighter liquid with which the heavier liquid is immiscible.

Example 1 A column yoi? crude oil 51 inches long is established in aglass tube standing vertically, having a bore of 0.5 inch. A quantity ofcarbon tetrachloride (Which is immiscible with the liquid to besupported), suflicient to increase the height of the oil column 23inches, is introduced into the .the length of the oil column about 30feet.

carbon tetrachloride-crude oil mixture. `immiscible liquid agent sointroduced, yremains tubing. After the carbon tetrachloride has settleddown into the oil column forming a relatively heavy solution in theupper part of the column, a quantity cf an oil-immiscible liquid agentto be supported thereon having a specific gravity of 1.13 sumcient toform a column 10 inches long in the tube is introduced. Theoilimmiscible liquid remains supported upon the carbon tetrachloridetreated oil column for approximately 20 minutes before the specificgravity of the solution in the upper part of the oil column declinesbelow that of the oil-immiscible liquid, allowing the oil-immiscibleliquid to drop through the oil column.

Example 2 An oil (crude oil) column is established in a string of 2 inchwell tubing standing vertically. Enough carbon tetrachloride (about 5gallons) is introduced into the top of the tubing to increase Severalgallons of a relatively heavy oil-immiscible .liquid agenty consistingof a resin forming liquid composed of a partially condensed mixture ofan `aldehyde and la phenol and capable of spontaneously hardening into asolid resin is introduced into'the tubing and allowed to descenduponfthe The oiloating upon'the'carbon tetrachloride-oil solu- .tion forapproximately one hour before the specolumn.

. 'Example 3 In'a'setup similar to that of Example 2, but using 2.5 inchtubing in p'lace of the 2 inch tubing, approximately '7.5 gallons ofcarbon tetrachloride is. introduced into the tubing string ahead of theoil-immiscible resin-forming liquid which remains .supported forapproximately one hour.

`While the foreging examples are illustrative of the manner in which therelatively heavy miscible liquid, interposed between the supportingliquid column and the relatively heavy immiscible liquid to-bevsupported may be used, it is to be understoodthat the `method is not tobe limited thereby, inasmuch as the method is effective with .otherliquids having similar characteristics as to .specic gravity,miscibility, and immiscibility,

Yand which occupies the uppermost position, and

the heaviest liquid (miscible) which occupies the position between thebottom of the column of the uppermost liquid and the top of the columnof :the lowermcst liquid, may be moved downn wardly and withoutalternation of their relative positionsin the tubing string, as when theliquid agentismoved into 'the well hole through the tubing string behindthe relatively light liquid column.

The invention may be further illustrated and explained by reference vtothe accompanying drawing in which:

vFig. 1 is a schematic elevational viewof an oil well provided with theusual casing and tubing, showing the well and tubing string partiallyiilled with oil.

Fig. 2 is a similar view to Fig. 1, showing the addition to the top ofthe oil column in the tubing string of a quantity of a relatively heavyoilmiscible liquid.

Fig. 3 is a similar View to Fig. 2, showing the addition to the tubingstring of the relatively heavy oil-immiscible liquid agentto besupported in the tubing string and kept separated from the oil columntherein.

Fig. 4 is a similar view to Fig. 3, and shows a subsequent stage in theuse of the principle of the invention.

In the several figures, like numerals designate 1 like parts.

Asshown inlFig. 1 the well bore I, extends from the surface of the earth2, through the earth stratum .3, to be treated. The well above thestratum 3, is provided with casing 4, cemented in place with cement 5.Suspended in the well through the casing head 6, is a string of tubing1,'the lower end 8, terminating opposite the stratum 3.

In carrying out the method in connection with the well illustrated, forexample, an oil column 8 is normally standing in the'tubing string I atthe commencement of the method (Fig. 1). A chargeiof a relatively heavyoil-miscible liquid is introduced into the' tubing 7, in an amountsufficient to increasethe'length of the liquid column 8, preferablybetween about 25 and 200 times the diameter of the bore of the tubingstring. With very small bores of tubing e. g. 0.5 inch, an increase inliquid column length of about 25 times the diameterof the'column4 issuicicntto provide aboutSO iminutes :of Asupporting time beforeintermixing may be expected. With bores of .2-to 2.5 inchesyan increasein liquid column length of about to 200 diameters is desirable. Afterintroducing the miscible heavy liquid into the tubing string, the liquidsettles down into the oil column 8, forming a heavy solution' 9, withthe upper part of column 8 (Fig. 2). The upper portion I0 of thesolution is essentially undiluted heavy liquid while the lower portionII of the solution is essentially all oil. Thereafter, the relativelyheavy oil 'immiscible liquid agent to be introduced into the well andkept separated from the oil column 8, is introduced into the tubingforming the liquid column I2 (Fig. 3). Being lighter than the liquid ofthe top I0 of the column 9, the liquid agent forming column I2, oats andremains floating as long as the relatively heavy butoil-miscibleliquidin column 9, does not become too highly diluted with the oil of the oilcolumn 8 .below it. As aforesaid, such support may be had for acomparatively long period of time. In the vExamples 2 and 3, at least anhour elapses before the supporting power of the liquid column G, is lostby dilution.

-Afourth liquid i3, (Fig. .4) of lower specific gravity than the liquidI2, may be introduced into the tubing string. for the purpose ofapplying pressure upon the liquids below it, so as to force the variousliquids into the well hole, as when it is desired to convey the liquidagent I2 through the tubing string into the Well hole I3, oppositestratum 3.

.As already indicated, the choice of separating liquid, referred tovgenerally heretofore as the relatively heavy miscible liquid, dependsupon the specific gravity of the lliquid agent to be supported and themiscibility of the separating liquid with the liquid of the liquidcolumn in the tubing string ahead ofiit. A wide choice of liquids isavailable for this use and their suitability for the purpose may beascertained readily by measuring the specific gravity of the liquidagent to be supported and choosing as a separating liquid any liquidhaving a higher speciiic gravity than the liquid agent and which ondissolving in the column of liquid in the well, forms a solution that isimmiscible with the agent to be supported. The following organic liquidsare heavier than and miscible with oil and are illustrative of thosewhich may be used on an oil column in the instances in which thespecific gravity of the liquid treating agent to be supported is lessthan the organic liquid chosen: ortho and meta dichlorobenzene, ortho,meta and para dibromobenzene, ethylene dichloride, trichloroethane,acetylene tetrachloride, pentachloroethane, trichloroethylene,,tetrachloroethylena trchloropropane, tetra chloropropane.

Among the advantages of the invention are, that the method prevents theintermixing of a relatively heavy liquid agent introduced into a Wellthrough the usual tubing string ahead of a lighter one with which theformer is immiscible irrespective of irregularities in the bore of thetubing string; and the use of tubing plugs is obviated along with theirattendant diiculties.

We claim:

1. In the treatment of a deep Well, provided with the usual tubingstring and having a column of liquid in the said tubing string, With aliquid agent which is immiscible with and of higher specific gravitythan the liquid of the said column of liquid and capable of penetratingan earth formation, the method of preventing the liquid agent fromdescending through and mixing with the liquid of the said column ofliquid on being deposited in the said tubing string which consists indepositing upon the said column of liquid, another liquid which ismiscible with the liquid of the said column oi liquid and of higherspecific gravity than the liquid agent in amount sufficient to increasethe specic gravity of at least the upper portion of the said column ofliquid to a value above that of the said liquid agent, and thereafterintroducing into the tubing string, the said liquid agent.

2. In the treatment of an oil well, provided with the usual tubingstring and having a column of oil standing in the said tubing string,with a liquid agent which is immiscible with and of higher specicgravity than the oil of the said column of oil and capable ofpenetrating an earth formation, the method of preventing the liquidagent from descending through and mixing with the oil column on beingdeposited in the tubing string which consists in depositing upon thesaid column of oil, a separating liquid which is miscible with and ofhigher speciilc gravity than the oil of the said oil column in amountsuil'icient to increase the specific gravity of at least the upperportion of the said column of oil to a value above that of the saidliquid agent, and thereafter introducing into the tubing string, thesaid liquid agent.

PAUL H. CARDWELL. ALBERT W. COULTER, JR. HARRY H. JONES.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,563,520 Owen Dec. l, 19251,889,889 Ennis Dec. 6, 1932 2,001,350 Mills May 14, 1935 2,122,452Clason July 5, 1933 2,316,596 Kennedy Apr. 13, 1943

1. IN THE TREATMENT OF A DEEP WELL, PROVIDED WITH THE USUAL TUBINGSTRING AND HAVING A COLUMN OF LIQUID IN THE SAID TUBING STRING, WITH ALIQUID AGENT WHICH IS IMMISCIBLE WITH AND OF HIGHER SPECIFIC GRAVITYTHAN THE LIQUID OF THE SAID COLUMN OF LIQUID AND CAPABLE OF PENETRATINGAN EARTH FORMATION, THE METHOD OF PREVENTING THE LIQUID AGENT FROMDESCENDING THROUGH AND MIXING WITH THE LIQUID OF THE SAID COLUMN OFLIQUID ON BEING DEPOSITED IN THE SAID TUBING STRING WHICH CONSISTS INDEPOSITING UPON THE SAID COLUNM OF LIQUID, ANOTHER LIQUID WHICH ISMISCIBLE WITH THE LIQUID OF THE SAID COLUMN OF LIQUID AND OF HIGHERSPECIFIC GRAVITY THAN THE LIQUID AGENT IN AMOUNT SUFFICIENT TO INCREASETHE SPECIFIC GRAVITY OF AT LEAST THE UPPER PORTION OF THE SAID COLUMN OFLIQUID TO A VALUE ABOUT THAT OF THE SAID LIQUID AGENT, AND THEREAFTERINTRODUCING INTO THE TUBING STRING, THE SAID LIQUID AGENT.